Having worked my way through college at a tire store, and having seen all types of sidewall damage, I can say as a general rule that if your sidewall isn't bulging (broken cords) or sliced down to where you can actually see the cords (they look like little white threads), you're probably in no immediate danger. If you can, however, the tire's trashed and you should stop driving on it immediately.

No matter what, you should have the tire checked out by someone who knows what they're looking for: better safe than sorry.Hope this helps.